446 Technique 70: Converting Numbers to Words

The main parts of the NumberToWords class are the entries (shown at 3 in the Listing 70-2) and the Convert method. The entries are simply extensions of the base RangeEntry class that process given ranges of the value being converted (the iVal parameter). The number is broken down by the increment of each range (thousands, hundreds, tens, ones) and each entry is called to process that particular unit. This continues until the input value is reduced to a value of zero. The loop to process the value is shown at 4.

Testing the Conversion Code

After you create a class, you should create a test driver that not only ensures that your code is correct, but also shows people how to use your code. The following steps show you how.

1. In the code editor of your choice, re-open the source file to hold the code for your test program.

In this example, I named the test program ch70.cpp.

2. Type the code from Listing 70-3 into your file.

Better yet, copy the code from the source file on this book’s companion Web site.

LISTING 70-3: THE NUMBER-CONVERSION TEST PROGRAM

int main()

{

NumberToWords nw;

string s1 = nw.Convert(123);

cout << “String: “ << s1 << endl; string s2 = nw.Convert(1);

cout << “String: “ << s2 << endl; string s3 = nw.Convert(23);

cout << “String: “ << s3 << endl; string s4 = nw.Convert(807);

cout << “String: “ << s4 << endl; string s5 = nw.Convert(123456); cout << “String: “ << s5 << endl;

}

The purpose of our little test driver is simply to show that the class works with all of the exceptional cases that exist for numeric conversions. For example, we want examples of ones, tens, hundreds, and thousands. We also want a simple example that requires the code to check all of its conditions, such as 23.

3. Save the source code in the code editor and then close the editor application.

4. Compile the source code with your favorite compiler, on your favorite operating system.

5. Run the program on your favorite operating system’s console.

If you have done everything properly, you should see the following output from the program on the console window:

$ ./a

String: one hundred twenty three String: one

String: twenty three String: eight hundred seven

String: one hundred twenty three thousand four hundred fifty six

As you can see from the output listing, the code works properly. All of the various scenarios are handled correctly and the output is in expected English. As mentioned previously, possible enhancements to the application would be extending the classes to process millions, billions, and so forth, or adding hyphens, if desired.

71 Reducing the

Complexity of Code

Technique

Save Time By

Componentizing your code

Restructuring programs

Specializing components

Programmers know the best program design is always simple. In fact, among programmers, the KISS principle has become a cliché: “Keep It Simple, Stupid.” To keep things simple, you have to follow three

basic principles when writing and maintaining code:

Componentizing

Restructuring

Specializing

By following these few simple processes when you develop and debug your code, you can drastically cut down on your maintenance time. In this technique, we will look at these four pillars of programming simplicity — and examine how to apply them.

A Sample Program

Imagine, for a moment, that you’re working on a program that parses input files for words. This sort of program might be used to get a list of words for a spell-checker or a stop list for an indexing program. In text indexing, a stop list gives the program a list of words to ignore when placing them in the index. The code for this type of program is shown in Listing 71-1. Its obviously a very simple, stripped-down program, but it illustrates the basic idea of what we’re trying to accomplish.

448	Technique 71: Reducing the Complexity of Code
LISTING 71-1: THE ORIGINAL WORD-PARSER PROGRAM
#include <stdio.h>
#include <string.h>
#include <vector>
using	namespace std;
void my_func( std::vector< char *>& words )
{
FILE *fp = fopen(“myfile.txt”, “r”);
if ( fp == NULL )
	return -1;
while ( !feof(fp) )
{	char szBuffer[ 81 ];
	memset( szBuffer, 0, 80 );
	if ( fgets( szBuffer, 80, fp ) == NULL )
	break;
	// Parse the line
	char szWord[80];
	memset ( szWord, 0, 80 );
	int pos = 0;
	for ( int i=0; i<(int)strlen(szBuffer); ++i )		1
	{

switch ( szBuffer[i] )

{

case ‘:’:

if ( strlen(szWord) )

{

char *str = new char[strlen(szWord)+1]; strcpy( str, szWord );

words.insert( words.end(), str ); szWord[0] = 0;

pos = 0;

memset ( szWord, 0, 80 );

}

break;

default:

szWord[pos] = szBuffer[i]; pos++;

break;

}

}

}

fclose(fp);

}

Componentizing 449

int main(int argc, char **argv )

{

std::vector< char *> words; my_func( words );

std::vector< char *>::iterator iter;

for ( iter = words.begin(); iter != words.end(); ++iter ) printf(“Word: %s\n”, (*iter) );

return 0;

}

The code above is supposed to read lines in from a file, parse them into words, and store the words in an array. It is assumed that the lines have a specific format: word1:word2:word3 followed by a carriage return. Given an input like that, the assumption is that the program will produce a list that contains word1, word2, and word3. The code accomplishes this by stepping through each character in the line, looking for a colon (:) and taking whatever precedes it as a word. You can see this code in the loop shown at 1.

This code generally works, except it has a rather severe bug — it will skip words at the end of a line — and anyway the real issue is that this code is hard to maintain. If we add a new separator to the line (for example), what happens? If someone comes along and has no idea what the code does, is it at all intuitive? The first step to making things better is to separate it into components.

If we run the program with an input file that looks like this

word1:word2:word3

line2:word2:word3

line3:word3:word4

The problem is shown by the fact that the word3 from line 1 and word3 from line 2 are not shown.

Componentizing

Componentizing is my own term for the process of splitting something up into components. In our code, there are two major components, a file component and a parser component. Components differ from functions, methods, or classes. A component is a single functional element — that is, a collection of code that accomplishes a single task or deals with a single area such as a file or parsing text. Componentizing simplifies your code by reducing the amount of cohesion between the various units of a module, and by limiting the areas in which you need to search for a given piece of functionality. If we are looking for something that reads from or writes to a file, we look in the file component. We wouldn’t bother to look in the parser component, because that has nothing to do with reading or writing from a file. We have not yet split our class into components, we are merely identifying the different units in the current code.

the program will then parse the individual lines into

Line1:

word1

word2

Line2:

line2

word2

The next step toward making our code simpler is to break it down into separate components. Let’s identify and split out the pieces into their own componentized classes. Our new structure will contain two separate classes. This is how you do it.

450 Technique 71: Reducing the Complexity of Code

1. In the code editor of your choice, create a new file to hold the code for the implementation of source file.

In this example, the file is named ch71.cpp, although you can use whatever you choose.

2. Type the code from Listing 71-2 into your file.

Better yet, copy the code from the source file on this book’s companion Web site.

LISTING 71-2: THE COMPONENTIZED SAMPLE PROGRAM

#include <stdio.h> #include <string.h> #include <vector> #include <string>

using namespace std;
class ParserFile		2
{

private: FILE *fp;

public:

ParserFile(void)

{

fp = NULL;

}

ParserFile( const char *fileName )

{

if ( fileName != NULL )

fp = fopen( fileName, “r” );

}

string getLine()

{

string s = “”;

if ( fp == NULL ) return s;

char c = 0;

while ( !feof(fp) && c != ‘\n’ )

{

c = fgetc(fp);

if ( c != ‘\n’ && c != ‘\r’ && c != EOF)

s += c;

}

return s;

}

bool eof()

{

if ( fp == NULL ) return true; return feof(fp);

}

};
class Parser		3
{
private:
char delimiter;
vector< string > words;
public:
Parser(void)
{
delimiter = ‘;’; // default
}
Parser( const char& delim )
{
delimiter = delim;
}
void clear()
{
words.erase( words.begin(),
words.end() );
}

bool parse( const string& in )

{

string sWord = “”;

if ( delimiter == 0 ) return false;

if ( in.length() == 0 ) return false;

for ( int i=0; i<(int)in.length(); ++i )

{

// End of word or string?

if ( in[i] == delimiter)

{

words.insert( words.end(), sWord );

sWord = “”;

}

else